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NCV8612 Datasheet(PDF) 11 Page - ON Semiconductor |
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NCV8612 Datasheet(HTML) 11 Page - ON Semiconductor |
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11 / 26 page  NCV8612 http://onsemi.com 11 and overshoot of output voltages. The soft−start function applies to all 3 regulators. The soft−start function kicks in for start up, start up via enable, start up after thermal shutdown, and startup after an over voltage condition. LDO3 is not subject to soft−start under all conditions. The LDO3 output is not affected by overvoltage shutdown, and therefore is not effected by the soft−start function upon the device’s return from an over voltage condition. Also, when VIN_S3 is connected to an independent supply and the supply is made available after the soft−start function, LDO3 will not have an independent soft−start. LDO1 Regulator The LDO1 error amplifier compares the reference voltage to a sample of the output voltage (VOUT1) and drives the gate of an internal PFET. The reference is a bandgap design to give it a temperature−stable output. LDO2 Regulator The LDO2 error amplifier compares the reference voltage to a sample of the output voltage (VOUT2) and drives the gate of an internal PFET. The reference is a bandgap design to give it a temperature−stable output. LDO3 Regulator The LDO3 error amplifier compares the reference voltage to a sample of the output voltage (VOUT3) and drives the gate of an internal PFET. The reference is a bandgap design to give it a temperature−stable output LDO3 is an adjustable voltage output. The adjustable voltage option requires an external resistor divider feedback network. LDO3 can be adjusted up to 10 V. The internal reference voltage is 0.996 V. To determine the proper feedback resistors, the following formula can be used: VOUT3 = VOUT3FB [(R1+R2)/R2] Figure 4. Feedback Network R1 R2 VOUTA FB VOUT3 Stability Considerations The output or compensation capacitors, COUTX help determine three main characteristics of a linear regulator: startup delay, load transient response and loop stability. The capacitor values and type should be based on cost, availability, size and temperature constraints. Tantalum, aluminum electrolytic, film, or ceramic capacitors are all acceptable solutions, however, attention must be paid to ESR constraints. The aluminum electrolytic capacitor is the least expensive solution, but, if the circuit operates at low temperatures (−25 °C to −40°C), both the value and ESR of the capacitor will vary considerably. The capacitor manufacturer’s data sheet usually provides this information. The value for each output capacitor COUTX shown in Figures 22 − 27 should work for most applications; however, it is not necessarily the optimized solution. Stability is guaranteed at the following values: COUT1 w 47 mF, ESR v 10 W COUT2 w 47 mF, ESR v 10 W COUT3 w 47 mF, ESR v 10 W Actual limits are shown in graphs in the Typical Performance Characteristics section. Thermal As power in the NCV8612 increases, it might become necessary to provide some thermal relief. The maximum power dissipation supported by the device is dependent upon board design and layout. Mounting pad configuration on the PCB, the board material, and the ambient temperature affect the rate of junction temperature rise for the part. When the NCV8612 has good thermal conductivity through the PCB, the junction temperature will be relatively low with high power applications. The maximum dissipation the NCV8612 can handle is given by: PD(max) = (TJ(max)−TA)/RthJA See Figure 20 for RthJA versus PCB Area. RthJA could be further decreased by using Multilayer PCB and/or if Air Flow is taken into account. IGNOUT Circuitry The IGNOUT pin is an open drain output Schmitt Trigger, externally pulled up to 5 V via a 10 k W resistor. The IGNOUT pin can be used to monitor the ignition signal of the vehicle, and send a signal to mute an audio amplifier during engine crank. The IGNIN pin is ESD protected, and can handle peak transients up to 45 V. An external diode is recommended to protect against negative voltage spikes. The IGNOUT circuitry requires the device to be enabled for proper operation. VPP Function The reset and warning circuits utilize a push−pull output stage. The high signal is provided by VPP. VPP is tied internally to LDO1. Under this setup, and any setup where LDO’s 1−3 are tied to VPP, loss of the VPP signal can occur if the pull up voltage is reduced due to over current, thermal shutdown, or overvoltage conditions. Reset Outputs The Reset Output is used as the power on indicator to the Microcontroller. The NCV8612 Reset circuitry monitors the output on LDO1. This signal indicates when the output voltage is suitable for reliable operation. It pulls low when the output is not considered to be suitable. The Reset circuitry utilizes a push |
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